Militants attacked international and Afghan security forces in southern Afghanistan on Tuesday, two days after gunmen in police uniforms opened fire on NATO troops, killing a service member.

NATO officials say seven insurgents breached the outer perimeter of the coalition base early Tuesday in Kandahar province, but that no coalition soldiers were killed. Initial reporting by Afghan officials had indicated at least one foreigner was killed and two others wounded.

Hours later in Kandahar city, Afghan authorities say four militants attacked a police checkpoint, killing at least three police officers. One of the gunmen also was killed.

Tuesday's violence comes days after individuals dressed in Afghan police uniforms turned their guns on NATO troops in Kandahar, killing a soldier before fleeing.

In recent months, there has been a series of attacks where Afghan security personnel or individuals dressed in police or army uniforms have opened fire on their international counterparts. At least 20 Western troops have been killed so far this year.

Meanwhile in Kabul, Afghanistan's Attorney General Mohammed Ishaq Aloko said "regional intelligence agencies" were involved in a suicide attack targeting Shi'ite Muslims in Kabul last year.

The December 6 attack outside a shrine in the Afghan capital killed at least 56 people. Pakistan-based militant group Laskhar-e-Jhangvi claimed responsibility for the blast.

On Tuesday, Attorney General Aloko told reporters that two men have been arrested for helping transport the suicide attacker from the northwestern Pakistani city of Peshawar to Kabul. He said the attack was planned in Peshawar and was supported by intelligence agencies in neighboring countries. Aloko did not give details.